Amplifier having frequency responsive variable gain



CCL 5, 1954 E EBERHARD 2,691,074

AMPLIFIER HAVING FREQUENCY RESPONSIVE VARIABLE GAIN Filed Aug. 3l, 1949 lcalma/v1? rwww $52 2a 515E t -S- L .7/ g I@ INVENTOR 5.1% 1 y EVERETT EBERHARD t BY f" SW L ATTORNEY A Facade/vc y Patented Oct. 5, i954 UNITED STAI!" OFFICE AMPLIFER HAVING FREQUENCY RESPNSWE VARIABLE GAIN Everett Eberhard, iiaddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware 4 Claims.

This invention relates generally to amplifiers of the semi-conductor type, and particularly ren lates to amplifiers of this type having a gain that is a function of frequency such, for example, as band-pass or band-rejection amplifiers.

'I'he three-electro-de semi-conductor amplifier is a recent development in the field of electronic amplification which does not require a vacuum tube. This device, which has been termed a transistor, has been disclosed in a series of three letters to the Physical Review by Bardeen and Brattain, Brattain and Bardeen, and Schockley and Pearson which appear on pages 230 to 233 of the July 15, 1948 issue. The new amplifier includes a block of a semi-conducting material such as silicon or germanium which is provided with two closely adjacent point electrodes called emitter and collector electrodes in contact with one surface region of the material, and a base electrode which provides a large-area, lowresistance contact with another surface region of the semi-conducting material. The semi-conductor amplifier may accordingly be considered a three-terminal network having one terminal common to the input and output circuits. Thus, the amplifier is essentially a four-terminal network which provides under proper operating conditions current amplification as well as voltage amplification.

In accordance with the present invention, it

has been found that the gain of a semi-conductor amplifier may be made a function of the frequency of the applied signal. Thus, it is feasible to provide band-pass amplifiers, or band-rejection ampliiiers which have substantially no gain Within a predetermined frequency range. Furthermore, the gain of the amplifiers may be made to rise or to fall with increasing frequency of the input signal.

It is accordingly the principal object of the present invention to provide novel amplifiers having a gain that is a function of the frequency of the input signal, such as band-pass amplifiers, band-rejection amplifiers, amplifiers having a cut-off at a predetermined frequency or amplifiers having a gain that either rises or falls with increasing frequency.

A further object of the invention is to provide semi-conductor amplifiers having internal feedback thereby to make the gain of such an amplifier a function of the frequency of the input signal.

A semi-conductor amplifier in accordance with the present invention has a reactive impedance element connected to either the emitter electrode cuit connected with the emitter electrode. A

band-rejection amplifier may include a parallel resonant circuit connected to the emitter electrode or a series resonant circuit connected to the base electrode. An amplifier having a gain which falls with increasing frequency may include ay capacitor connected with the base electrode. Alternatively, the same result may be obtained by connecting an inductor to the emitter electrode. i

An amplier having a gain which rises with increasing frequency may include either a capacitor connected with the emitter electrode or an y inductor connected with the base electrode. The input signal may be impressed on either the emitter electrode or on the base electrode while the amplified output signal is derived from the collector electrode. By connecting resonant circuits to all three electrodes of the amplifier it is feasibleto obtain a sharper pass band or rejection band or to obtain a sharper cut-off at a predetermined frequency.

The novel features that are considered charl acteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which:

Figure 1 is a schematic circuit diagram of a semi-conductor amplifier provided with external impedance elements which will be referred to in explaining the present invention;

Figure 2 is an equivalent network representing the amplier of Figure 1;

Figure 3 is a band-pass amplifier embodying the present invention and having a series resonant circuit connected to the emitter electrode;

Figure 4 is a graph illustrating the gain of the amplifier of Figure 3 as a function of frequency;

Figure 5 is an amplifier in accordance with the invention, having a gain that rises with frequency due to a capacitor connected to its emitter electrode;

Figure 6 is a graph illustrating the relative 3 gain of the amplifier of Figure 5 as a function of frequency;

Figure '7 is a band-rejection amplifier in accordance with the invention having a parallel resonant circuit connected to the emitter electrode;

Figure Sis agraph illustratingthefrelative gain of the ampliiier of Figure 7 as afunction of frequency;

Figure 9 is a modified amplifier of the invention having a gain that falls with increasing frequency due to a capacitor connected to its base electrode;

Figure 10 is a graph illustrating the relative gain of the ampliiier of Figure-v 9 as a function of frequency;

Figure 11 is a circuit diagram of an amplifier in accordance with the inventionhaving again that rises with frequency due to an inductor connected to its base electrode;

Figure 12 is a circuit diagram of a modified bandlZl-rejection, amplifier-in accordance with the.

invention;

Figuref 13'; isf a circuit diagram of a: band-pass amplierf embodying the present invention. and

havingv tuned,circuitaconnected to all of its; elec-- trodes, the input signalbeing impressed on the.

base electrode;

FigureV 14 isV a. circuit. diagram of; av modiiied bandi-pass amplifierI in accordancezwith the in vention having a. sharper-cut-off due to the provision ofl individual parallel .resonant circuitsconinected to the emitter. and base electrodes;

Figurev l5. isa graph illustrating. the relative gain of the amplier of Figure 14 as a. function of'frequency;`

Figure'l. is a circuit diagramof a band-passamplier having a series resonant circuit con:- nectedto theemitter-electrode to which the input signal is impressed; andv Figure 17 is a circuit'diagram of a modication offthe ampliiier-of-Figure 16 embodying thelpres'- ent invention and having a sharperv pass band than theamplier of Figure 16.'

Referring` now to the drawing; in which like components have been designated" by the same reference numerals throughout the iigures, andv particularly. to Figure-1, there'is illustrated'a semi-v conductorv amplifier. The amplier comprises body 2lof.l semi-conductingV material which may consist, for example, of boron, silicon, germanium, tellurium or selenium containinga small but sufficient number'of atomic impurity centers or lattice-imperfections as commonly employed for best results in crystal rectiers. Germanium is the preferredlmaterial for body 20`and may be preparedl so asj to be an electronic N type semiconductor, as is welll known. The surface of 'semiconducting'body 20 may, for'example, be polished and etched in the manner explained in the paper by Bardeen and Brattain referred to. It is also feasiblefto utilize the germanium blockn from a commercial high-back-voltage germanium rectier such as the typeA INSiin which case further surface treatment may not be required.

Semi-conducting body 2U' is'provided with emitter electrode 2l', collector electrode 22' and base electrode 23. Emitterelectrode 2| and collector electrode 22- are small-area electrodes and may be point contacts consisting, for-example, of tungstengoi'Phosphor bronze wires-having a diameter ofthe orderof 2 to 5 mils.- Emitter'an'd collector electrodes2 l, 221are ordinarily placed closely adjacent to each other eitheron-theV same surface of body or on opposite surfaces thereof andv they=may, befseparatedby a distance of from;2'to

5 mils. Base electrode 23 provides a large-area low-resistance contact, that is, a non-rectifying contact with the bulk material of semi-conducting body 20.

Separate resistors are provided in the leads of each of the three electrodes. Thus, base resistor ri is arranged between base electrode 23 and ground. Collector resistor 1'1. is provided between collector electrode 22 and battery 24 while emitter resistor re' is connected between emitter electrode 2l and battery 25. Battery 24 is provided' between ground and collector electrode 22 for the purpose of applying a relatively large reverse bias betweenv collector electrode 22 and base electrode 23. Battery 25 connected between ground and emitter electrode 2| applies normally a small forward bias between emitter electrode 2l and base electrode 23. It is believed that the operation of the circuit of Figure l is suiliciently well understood so as not, to require further explanation here. For/further explanatory material regarding, the operation of a semi-conductor iamplifier, reference is made tothe recent` paper by Webster, Eberhard and Barton whichappears on; pages 5 to 16 of the March 1949-issue of RCA Review.

Figure 2 illustrates an: alternating-current equivalent circuiti of the amplifier of Figure 1,

the equivalentl network beingdescribedzon page9` (Figure 4) ofthe paper by Webster, Eberhard and Bartonreferred to; In the circuitV of 'Fig ure` 2, dotted box 2 indicates semi-conducting body 20 which maybe considered as including resistor rb which appears looking into base electrode 23 between. the electrode and ground; re.- sistor.y re appearing looking into emitter electrode 2l between'v the electrode` andground; and resistor` rc1 which appears lookingy into collector electrode 22. between thecollector'and grcund In series with resistorrc and rr. there is provided an impedanceless generator labeled nnb, where i1 is the current flowing into the emitter electrode as-indicated-in Figure 2. i2 is the alternating current flowing from the collector electrode 22.

Letit be assumedthat the input signal is applied between base electrode 23. and'ground whileY the.v output signall is. derived between collector electrode 22 and ground. Forithis condition, a mathematical analysis of the circuits of Figures 1 and 2 may be carried out; Thus, it followsthat the input impedance looking into terminals 29 will approach ri whenV the followingy condition is met:

where rE=rel-1e'. The remaining symbols4 occurring in Formula 1 are indicated in Figure 2. Thisis simply the conditionof i1=i2 in Figure 2.

Under these operating conditions the voltage gain G is given bythe following formula:

G`=7L/TE (2) Similarly, thepowergain P, is given as follows:

It will now be seen that thevoltage gain is inversely proportional, to the; external emitter resistanceA re, the'power gain is inversely pro portioned to the square of the4 external emitter impedance ref if ref is large compared to re. Furthermore, the power gain is directly proportional' tofthel external base Iimpedance4 Ti.

Thevoltage andjpower gainl of the amplier Will.V increase..A over its normal gainV where i1=i2;

when the left hand term of Formula1 becomes greater than the right hand term. However, the practical gain is limited because when the point of oscillation is reached. the device will no longer amplify. It can be shown that with i1=i2 the point of oscillation will occur when n approaches infinity. Then as r1 is made larger, the condition of 1:2 approaches the condition for oscillation.

While the above mathematical treatment applies particularly to an amplifier where the input signal is impressed on the base electrode, somewhat similar conditions exist when the input signal is impressed on the emitter electrode. Consider the circuit of Figure 2 wherein re' is replaced by a voltage generator having a variable voltage e1 in series with a resistor Re. An analysis of this circuit has been carried out giving the following results. The condition of 1:2 is reached when:

Under these operating conditions the voltage ratio @o 7'L eI Ie'i`7'e (n) where e0 is the voltage developed across TL.

Under the above conditions it can again be shown that the point of oscillation approaches the point where i1=i2 as n increases. cates that for iz i1 the power gain varies directly with ri. However, when i1=z'z, the gain is not a function of ri.

It will readily be apparent from Equation 3 that the gain of the amplifier (with input between base electrode 23 and ground) of Figure 1 can be controlled if a frequency-dependent impedance element is connected to the emitter electrode 2|. Such an element Will control the internal feedback of the amplier which is determined by the external impedance in the base and in the emitter leads. An amplifier having a series resonant circuit 30 connected between emitter electrode 2| and ground is illustrated in Figure 3. At the resonant frequency of series resonant circuit 30 its impedance approaches zero accordingly the gain cf the amplifier of Figure 3 at that frequency is a maximum. As the frequency of the input signal deviates from the resonant frequency of circuit 30 the gain will decrease. .ficcordinglyg the amplifier of Figure 3 functions as a band-pass amplifier.

Battery 2d of the amplifier of Figure 3 may be by-passed for signal frequencies by capacitor 3| and may be connected to collector electrode 22 through load resistor 32. Battery 25 is similarly bypassed by capacitor 33 for signal frequencies and may be connected to emitter electrode 2| through resistor 33 and inductor 35 of resonant circuit 30. One terminal of capacitor 33 which, together with inductor 35, forms series resonant circuit 30, may be grounded. The input signal may be impressed on input terminals 31 connected across base resistor 38 which may be grounded as shown.

Figure 4 shows curve 40 representing the relative gain of the amplier of Figure 3 with respect to frequency. As pointed out hereinabove the gain is a maximum at the resonant frequency of series resonant circuit 30. The amplified output signal may be derived from output terminals 4| connected effectively across load resistor 32.

The input and output impedances of the amplifier of Figure 3 are substantially the same.

This inde allel resonant circuit 41.

Accordingly, two ampliler stages can be connected in cascade without requiring impedance matching networks. In order to provide good stability of the amplifier of Figure 3 the following condition should be fulfilled:

7Li-rc should be unity or slightly less and base resistor 33 should be less than 10,000 ohms.

It is also feasible to connect a reactive impedance element to emitter electrode 2|. Thus, Figure 5 illustrates capacitor 43 connected between emitter electrode 2| and ground. The input signal to be amplified may again be impressed on input terminals 31 connected across base resistor 38. The output signal may be obtained from output terminals 4| one of which is grounded while the other one is coupled to collector electrode 22 through coupling capacitor 44.

The reactive impedance of a capacitor is proportional to the reciprocal of the frequency at which the impedance is measured. Since the gain of the amplier is inversely proportional to the external emitter impedance ref the amplifier of Figure 5 has a gain that rises with increasing frequency as illustrated by curve 45 of Figure 6. This rising gain characteristic may be utilized to compensate the normally falling gain of a semi-conductor amplifier. It may be pointed out that in the circuit of Figure 5 this principle of controlling response is valid only when the signal is impressed on base electrode 23 as illustrated.

The impedance of capacitor 43 should be appreciable at the signal frequency but is low compared to the resistance of resistor 34. It is also feasible to provide capacitor 46 connected in shunt with base resistor 38. Capacitor 4B, however, is optional and should have an impedance over the desired band of frequencies that is high compared to the resistance of resistor 38. The purpose of capacitor 46 is to prevent high-frequency oscillations by decreasing the impedance between base electrode 23 and ground at high frequencies.

From the above formulas it will be evident that it is also feasible to connect a parallel resonant circuit such as circuit 41 to emitter electrode 2| as illustrated in Figure '7. Battery 25 and resistor 34 may be connected in series with parallel resonant circuit 131 between emitter electrode 2| and ground. Capacitor 33 may bypass both battery 25 and resistor 34. The input signal is again impressed through input terminals 31 to base resistor 33 while the output signal is obtained from output terminals 4| connected across collector load resistor 32.

The reactive impedance of a parallel resonant circuit approaches infinity at its resonant frequency. Accordingly, as illustrated by curve 50 of Figure 8 the gain of the amplifier of Figure 7 is a minimum at the resonant frequency of par- The amplifier of Figure 7 accordingly is a band-rejection amplifier. Experiments have shown that a sharp rejection band can be obtained with the amplifier of Figure 7. The input signal in the amplifier of Figure 7 can only be impressed on the base electrode 23 as illustrated.

As has been already pointed out the power gain given by Formula 3 is directly proportional to the external base impedance n for a base input amplifier. Thus, the gain of an amplifier can -be controlled l by fproviding -'a capacitor *5l between baseelectro'de2-3 and-"ground `as shown iii-Figure 9. Capacitor5l may'beshunte'dby basefresistor 38 and-may? have 'an appreciable impedance for signal '-frequencies. The input signal may be impressed on input terminals 52, one of which is grounded while the other one is connected to base electrode 23 through series resistor l53. Resistor 53 indicates `schematically an impedance'provided in series 'with the source thereby to provide a high impedance input source. It is also feasible to impress the input signal on input terminals 54, one of which is grounded while the other one is coupled to emitter electrode 2| through coupling capacitor 55. This 'readily'follows from'the V,discussion of Formulas 4and5. The outputsignal may be derived from output terminals il coupled across load resistor V32.

Since the reactive impedance of the -capacitor decreases with frequency and since the gain ofthe ampliiier is `directly proportional to `the external: base impedance rethe gain'of the. amplifier of Figure 9 will decrease with an increase of frequency as illustrated bycurve '56 of Figure 10. VAs indicated in Figure yQthe input signal may be impressed on either base electrode 23 or on emitter electrode2l.

An amplier having a gain which decreases with an increase of frequency as illustrated in Figure 10 may also be obtained if an inductor is connected to the emitter. Thus it is feasible to omit capacitor in the circuit ofFigure 3. The falling gain is then determined by inductork 35 connected to emitter electrode 3 l.

It is also `feasible in accordance with the invention to provide an inductor Sn in the base lead as shown in Figure 11. `Inductor S9 preferably is connected in series with base resistor 38 between base electrode 23 and ground. The input signal may be impressed on input terminalsZ, one of whichv is grounded while the other one is connected to base electrode 23 through series resistor 53. 1t is also feasible to impress the input signal on input terminals 54, one of which is coupled to emitter electrode 2|.

VThe reactive impedance ofan inductor such as inductor is directly proportional to the frequency. Accordingly, the gain of the ampliiier of Figure 11 rises with increasing signal fre quency as illustrated bycurve of Figure 6. As illustrated inFigure 11 the input signal may lue-impressed on either base electrode 23 or. on emitter electrode 2 l.

Figure 12 illustrates still another-band re" jection amplier in accordance with the invention. The amplifier of Figure 12 has an output resistor 32 connected between battery 24 and collector electrode 22. Resistor 34 is connected Vbetween emitter electrode 2l and battery `25. In .accordance with the present invention, series resonant circuit GEI is connected between base electrode 23 and` ground. Circuit .86 comprises induct-or 8l Aand capacitor 82 which is bypassed by resistor .B3 to provide a direct current path between base electrode 23 and ground. In view of the factthat'the'external base'lea'dincludes considerable resistance, battery 25 should be so poled that its negative terminals connected toemitter electrode'2l.

The amplifier of Figure 12 is a band rejection amplifier having a response curve such as shown at in Figure l8. lThe operation ofthe ampli- Iier 'of vFigure I2 `follows 'from 'Formula `3 'provided the input signal is impressed on input terminals 3l connected between base electrode 23 and ground. In this case, r1 approacheszero for frequencies within the rejection band. The output signal may be obtained from outputf'terminals 4|.

It is also `feasible`to impress the-input'signal on input terminals 54, one of which is coupled to emitter electrode 2| through coupling capacitor'55. Thefmode of operation'ofthe amplier with emitter inputvreadily follows from Formulas 4, 5 `and the subsequent discussion. It should be pointed out, however,that the amplier should be operated so that i2 i1.

A modified band-pass amplier inaccordance with the invention which is similar to that of Figure 3, is illustrated in Figure 13. Thus,=series resonant circuit 3l! may be connected between emitter electrode 2l andground. Battery 25 and emitter resistor 34 may be connected in parallel with series resonant circuit 30. A parallel resonant circuit 63 is connected between base electrode 23 and ground. Parallel resonant circuit 64 may be connected between collector electrode 22 and collector resistor 32 and battery 24 connected in series. The input signal maybe impressed on input. terminals 3'! connected across parallel resonant circuit 63. The amplified output signal may be obtained from resonant circuit 35 inductively coupled to resonant circuit 64.

The output impedance of the amplifier should be large such as the impedance of parallelresonant circuitsl and. When all three resonant circuits 30, 53 and 64 are tuned to the same frequency a very selectivepass vband may be obtained. Thus, when the three resonant circuits aretuned to 455 kc. (kilocycles) a gain curve (Figure 4) 4 kc. wide was measuredr at the half power points.

The amplifier of Figure 13 functions as a bandpass amplifier having a sharper cut-olf on both sides of the resonant frequency of circuits 30, 63 and 64 than the amplifier of Figure 3. This is due to the fact that the three tuned circuits provide a sharper rejection at both sides of the pass band.

The amplier of Figure 14 is a band-pass ampliiier having a very sharp cut-olf at a predetermined frequency which is at one side of the pass band. To thisend, parallel resonant `circuit 4l is connected between emitter electrode 2i and ,resistor .34 and battery 25 connected in series. Another parallel resonant circuit G3 is connected between base electrode 23 and ground. The input signal may be impressed on input terminals .3l connected across parallel resonant circuit B3. '.Theoutput signal may be developed in parallelcircuit 64 connected in series between collector electrode 22 and battery 24. The amplified output signal may be obtained from output circuit G5 inductively coupled to resonant circuit 64.

The operation of the amplierof Figure 14 may best be understood by reference to Figurel. Thus, curve 1G shown in dotted lines indicates the gain of the amplifier if circuit 63 were omitted. Curve l0 corresponds to curve 50 of Figure '8 which indicates a band rejection amplier. Dot and dash curvell of Figure 15 indicates the ,gain of the amplifier due to parallel Aresonant'circuit 63. If resonant circuits 63 and 4l are tuned re- `spectivelyto frequencies f1 and 'fz as indicated in Figures f 14 and' 1'5; the resultant gain is shown by curve l2 in full lines. Accordingly, a very sharp cut-oif is obtained at one side of the pass band between frequencies f1 and f2, that is, between the frequencies to which circuits 63 and di are tuned. Resonant circuit 6d should be tuned to the frequency f1 to which resonant circuit 63 is tuned.

It follows from Equation that it is also feasible to impress the input signal on emitter electrode 2l in a band-pass amplifier of the type illustrated in Figure 3. Such band pass ampliers are shown in Figures 16 and 17. In this case, a low impedance driving source is required but a very high power gain may be realized. The input signalin the amplifier of Figure 16 may be impressed on parallel resonant circuit 75 which is loosely7 coupled to coil 35 forming part of series resonant circuit 30 connected between emitter electrode 2| and ground. Battery 25 and resistor 34 may be connected in shunt with series resonant circuit 3d. As shown in Figure '16 a base impedance element such as resistor 38 may -be required. The output signal may be developed in parallel resonant circuit i3d connected between collector electrode 22 and resistor 32 and battery 24. The output signal may be obtained from output terminals M. As illustrated in Figure 17 the base impedance element may also consist of parallel resonant circuit 63. If the three resonantl circuits S, 63 and $4 are tuned to the same frequency a very high selectivity may be obtained. The band-pass amplier of Figure 17 otherwise functions like that of Figure 16.

There have thus been disclosed semi-conductor amplifiers having a gain that is a function of the frequency of the input signal. The amplifiers may be arranged to have band-pass or bandrejection characteristics. Furthermore, ampliers may be provided which have a gain that either rises or falls with increasing frequency of the input signal. The input signal may be impressed on the base electrode or in some cases on the emitter electrode while the amplified output signal is derived from the collector electrode. A band-pass ampliiier has also been disclosed having a very sharp rejection at a predetermined side of the pass band.

What is claimed is:

l. A semi-conductor amplifier including a semiconducting device having a semi-conducting body, an emitter electrode, a collector electrode and a base electrode in contact with said body, said emitter and base electrodes being the input electrodes, said collector electrode and one of the other electrodes being the output electrodes of said amplifier, said device having a ratio of shortcircuit collector current increments to emitter current increments which, under proper operating conditions, does not substantially exceed unity, means establishing said operating conditions including a source of potential for applying energizing potentials to all of said electrodes, a rst parallel resonant circuit coupled between said nput electrodes for applying an input signal thereto, a second parallel resonant circuit connected between said output electrodes for deriving an output signal from said output electrodes, and a series resonant circuit connected between said emitter electrode and said nrst parallel resonant circuit to render the gain of said amplifier a function of the frequency of said input signal.

2. A semi-conductor amplier including a semiconducting device having a semi-conducting body, an emitter electrode, a collector electrode and a base electrode in contact with said body, said emitter and base electrodes being the input electrodes, said collector electrode and one of the other electrodes being the output electrodes of said amplier, said device having a ratio of shortcircuit collector current increments to emitter current increments which, under proper operating conditions, does not substantially exceed unity, means establishing said operating conditions including a source of potential for applying energizing potentials to all of said electrodes, means including a parallel resonant circuit connected between said input electrodes for applying an input signal to said input electrodes, means including a first resonant circuit coupled between said output electrodes for deriving an output signal from said output electrodes, and a second resonant circuit connected between said emitter electrode and said parallel resonant circuit, said parallel resonant circuit thereby presenting an appreciable impedance to said input signal, whereby the power gain P of said amplier is determined in accordance with the formula Ti TL TE TE where ri is the external base impedance, and TL is the external collector impedance and rE is the sum of the external emitter impedance and the internal emitter resistance, so that said power gain is a function of the effective impedance which said parallel resonant circuit presents to said input signal.

3. A semi-conductor amplifier including a semi-conducting device having a semi-conducting body, an emitter electrode, a collector electrode and a base electrode in contact with said body, said emitter and base electrodes being the input electrodes, said collector electrode and one of the other electrodes Abeing the output electrodes of said amplifier, said device having a ratio of short-circuit collector current increments to emitter current increments which, under proper operating conditions, does not substantially exceed unity, means establishing said operating conditions including a source of potential for applying energizing potentials to all of said electrodes, means including a parallel resonant circuit connected between said base electrode and a point of fixed reference potential for applying an input signal to said input electrodes, means including a resonant circuit connected between said collector electrode and said point of fixed reference potential for deriving an output signal from said output electrodes, and a series resonant circuit connected between said emitter electrode and said point of fixed reference potential, whereby the power gain P of said amplifier is determined in accordance with the formula p-i E' TE TE where r1 is the external base impedance, n is the external collector impedance and TE is the sum of the external emitter impedance and the internal emitter resistance, so that said power gain is a. function of the effective impedance which said series resonant circuit presents to said input signal.

4. A band pass amplifier comprising a semiconductor device including a semi-conductor body, a base electrode and an emitter electrode and a collector electrode in contact with said body, said device having a ratio of short-circuit 1li collector current ncrementsto emitter current increments which,` under proper operating conditions, does not substantially exceed unity, means establishing said operating conditions including a source of potential-for applying energizing potentials to said electrodes, a seriesresonant circuit connected between said emitter electrode and a point of xed reference potential, a first parallelresonant circuit connected between saidA collector electrode and said-point of xed 10 reference potential, a second parallel resonant circuit connected between said base electrode and said point of xed reference potential, said resonant circuits being tuned to the same frequency, means for impressing aninput signal on said second-parallel resonant circuit, and means for deriving an ampliedoutput vsgnalfrom said rst parallel resonant. circuit..

2 References: Cited in theleof this patent UNITED STATES PATENTS Number Name Date 2,351,934 Kramolin June 20, 1944 2,476,323 Rack July 19,4 1949 2,486,776 Barney Nov. 1, 1949 2,524,035 Bardeen et al. Oct. 3, 1950 2,541,322 Barney Feb. 13,1951 2,550,518 Barney Apr. 24, 1951 2,556,286l Meacham June l2, 1951 2,647,957 Mallinckrodt Aug. 4,1953 2,647,958' Barney Aug. 4, 1953Y OTHER; REFERENCES,

Article by Atkins inv Radio and Television News, October 1948, pp. 39, 181, 182,I 183, 184. Copy'in 179-17'1-MB5 

